This invention relates to a liquid-impervious backsheet for a body fluids disposal article such as a disposable diaper or a sanitary napkin.
Japanese Patent Application Disclosure No. 1993-200063 disclose a breathable liquid-impervious backsheet of a disposable diaper having, at least on one surface thereof, rough surface regions comprising a plurality of microprotuberances formed by grains of inorganic filler and relatively smooth surface regions wherein the rough surface regions include breathable micropores each having a diameter of 0.03xcx9c5 xcexcm.
With this known sheet, the rough surface regions are intended to conceal an absorbent core of the article soiled with body fluids and the smooth surface regions having a see through property are intended to tell the article user of a proper timing for exchanging the used article with a fresh one.
The Japanese Patent Application Disclosure No. 1993-200063 discloses such sheet particularly as used as the backsheet of the disposable diaper. The rough surface regions partially underlie the absorbent core and, in such zones, the absorbent core may cover the micropores to make their breathability ineffective. On the other hand, some of the micropores crowded in the rough surface regions may be connected one to another until they form a pore having a sufficiently large diameter to be moisture-pervious and consequently the body fluids may leak therethrough.
It is an object of this invention to provide an improved liquid-impervious backsheet adapted to maintain a desired breathability and, at the same time, to prevent body fluids from leaking.
According to this invention, there is provided an improvement of liquid-impervious backsheet for a body fluids disposal article having upper and lower surface and made of thermoplastic synthetic resin.
The improvement of this invention is in that the sheet comprises a plurality of independent concave zones depressed downward from the lower surface and a smooth zone extending around said concave zones, each of the concave zones is formed except a peripheral edge thereof with at least one micropore.
According to one embodiment of this invention, at least an upper surface of the sheet is water repellent in the concave zones and at least the upper surface of said sheet is hydrophilic in the smooth zone.
According to another embodiment of this invention, the number of the concave zones per 10 cm2 of the sheet is in a range of 4xcx9c100, a throat-area of each of the concave zones is in a range of 0.002xcx9c2.0 cm2, an intercentral distance of each pair of adjacent the concave zones is in a range of 0.1xcx9c1.5 cm and a height as measured from the lower surface of the sheet to a lower surface of a bottoms in each of the concave zones is in a range of 0.01xcx9c0.3 cm.
According to still another embodiment of this invention, a thickness of the sheet is in a range of 10xcx9c100 xcexcm and an inner diameter of each of the micropores is in a range of 0.05xcx9c1.0 mm.